Method And System For Maintaining Substantially Uniform Pressure Between Rollers Of A Printer

ABSTRACT

A method and system for maintaining a substantially uniform pressure between a pair of rollers is disclosed.

BACKGROUND

In a conventional offset printer, a series of rollers transfers ink inthe form of an image from roller to roller until the ink is finallytransferred onto a media. In this process, the media is fed into apressure nip formed between the last two rollers, sometimes referred toas a transfer roller and a media roller. In most instances, the transferroller includes a blanket, such as an electrically conductiverubber-coated fabric, for transferring the ink to the media. However,the blanket is typically secured to a cylinder of the transfer rollervia a clamp or other fastening mechanism, which introduces adiscontinuity on the surface of the transfer roller.

Unfortunately, this discontinuity disrupts a sensitive pressuredistribution between the transfer roller and media roller when thediscontinuity of the transfer roller engages the media roller. Amongother problems, this disruption affects the quality of the printing onthe media, resulting in problems such as banding on the media in areasof the media that pass adjacent to the discontinuity of the transferroller.

Accordingly, conventional printers fall short of desired printingquality by failing to compensate for these discontinuities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is side view schematically illustrating a printing system,according to one embodiment of the present disclosure.

FIG. 2 is schematic illustration of a control system, according to oneembodiment of the present disclosure.

FIG. 3 is an enlarged sectional view schematically illustrating apressure nip between a transfer roller and a media roller of theprinting system, according to one embodiment of the present disclosure.

FIG. 4 is an enlarged partial sectional view schematically illustratinga transfer roller of the printing system, according to one embodiment ofthe present disclosure.

FIG. 5 is a diagram schematically illustrating a linear spring model fora coupling mechanism of a roller, according to one embodiment of thepresent disclosure.

FIG. 6 is a diagram illustrating a gap setpoint profile, according toone embodiment of the present disclosure.

FIG. 7 is a diagram illustrating a gap differential profile, accordingto one embodiment of the present disclosure.

FIG. 8 is a flow diagram illustrating a method of producing a gapsetpoint profile, according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments which may be practiced. Inthis regard, directional terminology, such as “top,” “bottom,” “front,”“back,” “leading,” “trailing,” etc., is used with reference to theorientation of the Figure(s) being described. Because components ofembodiments of the present disclosure can be positioned in a number ofdifferent orientations, the directional terminology is used for purposesof illustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present disclosure. Thefollowing Detailed Description, therefore, is not to be taken in alimiting sense, and the scope of the present disclosure is defined bythe appended claims.

Embodiments of the present disclosure are directed to maintaining asubstantially uniform pressure between a first roller and a secondroller of a printer. In one embodiment, the first roller and the secondroller comprise a transfer roller and a media roller, respectively,which are in rolling contact with each other to form a pressure nip fortransferring an ink image onto a media passing through the pressure nip.In other embodiments, the first roller and the second roller comprise apair of rollers of a printer other than a transfer roller and/or a mediaroller and that are in rolling engagement with each other.

In one embodiment, the transfer roller comprises a cylinder (i.e. drum)and a blanket wrapped around the cylinder. In one aspect, with pressureapplied by the media roller, the blanket of the transfer roller iscompressed against an outer surface of the cylinder of the transferroller resulting in the blanket having a compressed thickness in thatregion. In one aspect, the thickness of the compressed region of theblanket defines a distance of separation between the media (as carriedon the media roller) and the cylinder of the transfer roller. Forpurposes of this application, this distance of separation between themedia and the cylinder of the transfer roller is referred to as a gapand is an indirect measure of the amount of compression of the blanket.Nevertheless, it is understood that the gap does not represent an actualvoid because the media roller is in rolling contact with the blanket ofthe transfer roller and the media interposed therebetween. Accordingly,in one aspect, this gap (between the media and the cylinder of thetransfer roller) plus the amount of compression of the blanket at thenip is substantially equal to the uncompressed thickness of the blanket.

In one aspect, a position of a rotational axis of the media roller ismovable for translation of the media roller towards and away from afixed position of a rotational axis of the transfer roller. Thisselective translation of the media roller enables controlling the gapand thereby controlling an amount of pressure applied at the pressurenip between the transfer roller and the media roller. In another aspect,translation of the media roller enables adjusting the pressure at thenip for different thicknesses of the media. With this in mind, in orderto obtain high quality printing on the media, a substantially uniformgap should be maintained between the media roller (with the mediacarried thereon) and the transfer roller.

In one embodiment, an outer surface of the transfer roller includes aseam, such as a recess configured to enable clamping of the blanket onthe cylinder of the transfer roller. In another embodiment, the mediaroller includes a seam. In yet other embodiments, both the media rollerand the transfer roller include a seam. However, it is understood thatin some embodiments, the seam may also comprise a raised protrusioninstead of a recess and/or the seam may be unrelated to clamping of ablanket.

Nevertheless, a substantial majority of the blanket is free of suchseams, and therefore the seam acts as a discontinuity that creates largedisturbances on the force and position between the transfer roller andthe media roller. These large disturbances disrupt maintaining asubstantially uniform gap, which in turn disrupts application of asubstantially uniform pressure between the media roller and the blanket.

In another aspect of the roller system of the printer, a couplingmechanism is interposed between the cylinder of the media roller and anaxle from a motor that causes translation of the media roller. Becausethis coupling mechanism exhibits elastic properties and generallydeforms due to the force exerted between the media roller and thetransfer roller, further difficulty is encountered in maintaining asubstantially uniform gap and thereby in maintaining a substantiallyuniform pressure. In particular, in attempting to achieve or maintain asubstantially uniform gap, conventional systems fail to account for agap differential or difference that exists between the actual gap(between the transfer roller and the media roller) and a gap setpointwith the gap differential being caused by the deformation of thecoupling mechanism.

Nevertheless, because the deformation of the coupling mechanism remainsgenerally constant in non-seam areas of the transfer roller,conventional encoder-based positioning mechanisms perform reasonablywell in controlling the gap in non-seam areas of the transfer roller andtherefore tend to maintain a substantially uniform pressure between themedia roller and the transfer roller in non-seam areas.

On the other hand, the deformation of the coupling mechanism can varydramatically in seam areas of the transfer roller. Unfortunately, thesesame conventional encoder-based positioning mechanisms are inadequate tocompensate for the large force and position disturbances caused by theinteraction of the seam of the transfer roller against the media roller.In one aspect, this force disturbance causes rapid deformation of theabove-described coupling mechanism because of the elasticity of thecoupling mechanism. Unfortunately, the conventional encoder-basedpositioning mechanisms are not capable of measuring this deformationbecause they are coupled to the axle of the motor causing the abovementioned translation. Therefore, they cannot provide a feedback signalwhich could be used to counteract the effect of this deformation.

However, embodiments of the present disclosure include a mechanism foradjusting the relative spacing between the transfer roller and the mediaroller to dynamically control the gap at the seam of the transfer rollerto overcome the large change in the gap differential that wouldotherwise be caused by the elasticity of the coupling mechanism. Thisdynamic gap control mechanism thereby minimizes the force and positiondisturbance that would otherwise be caused by interaction of the seamwith the media roller. In one aspect, this dynamic gap control mechanismis independent of, but operates in cooperation with, the conventionalencoder-based positioning mechanism.

In one embodiment, the dynamic gap control mechanism maintains aconstant gap setpoint in non-seam areas of the transfer roller butalters the gap setpoint when seam areas of the transfer roller interactwith or engage the media roller. In particular, the gap setpoint istemporarily increased in the seam areas to counteract unwanted changesin the gap differential (due to the varying value of the deformation ofthe coupling mechanism of the media roller). By better controlling thegap differential in the seam areas of the transfer roller, this dynamicgap control mechanism enables maintaining a substantially uniform gapabout an entire circumference of the respective media and transferrollers despite the presence of the seam(s) on the transfer roller.

Accordingly, embodiments of the present disclosure maintain asubstantially uniform pressure between the media roller and a transferroller despite one or more seams on a surface of transfer roller, whichin turn enables consistent, high quality printing.

These embodiments, and additional embodiments, are described inassociation with FIGS. 1-8.

One embodiment of a printing system 10 including a printer 12 isillustrated in FIG. 1. As shown in FIG. 1, printer 12 comprises a laserimager 20, an imaging roller 30, a transfer roller 40, and a mediaroller 42. In addition, the printer 12 comprises a charging station 32,a developing station 34, and a controller 50. In one aspect, the imagingroller 30 includes an outer electrophotographic surface or plate 31while the transfer roller 40 includes a blanket 44.

While not shown in FIG. 1, in other embodiments the printer 12additionally comprises excess ink collection mechanisms, cleaners,additional rollers, and the like as familiar to those skilled in theart. A brief description of the operation of the printer 12 follows.

In preparation to receive an image, the imaging roller 30 receives acharge from charging station 32 (e.g., a charge roller or a scorotron)in order to produce a uniform charged surface on the electrophotographicsurface 31 of the imaging roller 30. Next, as the imaging roller 30rotates (as represented by directional arrow A), the laser imager 20projects an image via beam 22 onto the surface 31 of imaging roller 30,which discharges portions of the imaging roller 30 corresponding to theimage. These discharged portions are developed with ink via developingstation 34 to “ink” the image. As imaging roller 30 continues to rotate,the image is transferred onto the electrically biased blanket 44 of therotating transfer roller 40. Rotation of the transfer roller 40 (asrepresented by directional arrow B), in turn, transfers the ink imageonto media M passing through the pressure nip 62 between transfer roller40 and media roller 42.

While not shown in FIG. 1, it is understood that in another embodimentmedia roller 42 also acts as the media supply with the media M beingwrapped about a cylinder 43 of media roller 42 to form the outer portion45 of media roller 42. In yet another embodiment, media roller 42 isconfigured to releasably secure media M to a surface of media roller 42as media M passes through the pressure nip 62 so that media M is wrappedaround media roller 42 at pressure nip 62.

FIG. 2 is a schematic illustration of a roller control system 100 of aprinter, according to one embodiment of the present disclosure, whichprovides further details regarding the interaction of a media roller anda transfer roller. In one embodiment, roller control system 100 formspart of a printer comprising substantially the same features andattributes as printer 12 previously described in association withFIG. 1. In one aspect, roller control system 100 comprises a rollerportion 101 including a transfer roller 102 and a media roller 104 thathave at least substantially the same features and attributes as transferroller 40 and media roller 42 of FIG. 1, respectively.

As shown in FIG. 2, transfer roller 102 is rotatable about axis 110 (asrepresented by arrow B) and includes a cylinder 112 with a blanket 114secured onto cylinder 112. Axis 110 allows rotation of cylinder 112 butis otherwise fixed. In one aspect, a coupling mechanism 111 is disposedat least one end of cylinder 112 (e.g. drum) as schematicallyillustrated in FIG. 2 and is configured to couple cylinder 112 relativeto an axle of the rotation motor 150 that controls rotation of transferroller 102. In addition, FIG. 2 schematically illustrates a rotationallink 151 associated with coupling mechanism 111. The rotational link 151extends between transfer roller 102 and media roller 104 to transfer therotational motion of transfer roller 102 to the media roller 104. Inthis way, rotation of media roller 104 is controlled via rotation oftransfer roller 102. However it is further understood that otherarrangements of controlling the rotation of transfer roller 102 andmedia roller 104 will be recognized by those skilled in the art.

In another aspect, cylinder 112 is formed of a metallic material andblanket 114 is formed of a conductive rubber material (or otherconductive, elastic material) to enable cylinder 112 to electricallybias blanket 114. In another aspect, transfer roller 102 comprises atleast one seam 116 positioned within non-seam area 117, which otherwisegenerally defines a substantial majority of the circumference of thetransfer roller 102. As shown in FIG. 2, seam 116 comprises a recessincluding a first edge 118, an intermediate portion 122, and a secondedge 120. In one aspect, among other functions, seam 116 is configuredto secure a clamp or other fastening mechanisms to secure blanket 114about cylinder 112. Accordingly, the position of blanket 114 generallycorresponds to non-seam area 117 of transfer roller 102.

In another aspect, it is also understood that second edge 120 of seam116 generally corresponds to a leading edge of a media M (e.g., such asa sheet) while first edge 118 of seam 116 generally corresponds to atrailing edge of a media M.

It is understood that in other embodiments, seam 116 may comprise aprotrusion rather than a recess. In yet other embodiments, seam 116 isnot exclusively associated with clamping a blanket 116 about cylinder112 but comprises other geometrical variations or topographical featuresof transfer roller 102. Moreover, in other embodiments, media roller 104also may include a seam 116. In yet other embodiments, both media roller104 and transfer roller 102 include one or more seams 116.

As shown in FIG. 2, seam 116 extends generally parallel to a rotationalaxis (or a longitudinal axis) of the transfer roller 102. In oneembodiment, seam 116 extends along at least a majority of a length ofthe transfer roller 102. In some embodiments, the seam 116 extendsthrough a thickness of the blanket 114 and at least partially into thecylinder 112, as shown in FIG. 2.

Media roller 104 is rotatable about axis 124 (as represented by arrow C)and comprises a cylinder 120 which is configured to carry media 122through an interaction zone 127 between media roller 104 and blanket 114of transfer roller 102. In one aspect, a coupling mechanism 125 isdisposed at one end of cylinder 120 as schematically depicted in FIG. 2and is configured to couple cylinder 120 relative to an axle of atranslation motor 154 that controls the translation of media roller 104relative to transfer roller 102.

In another aspect, when non-seam areas 117 of transfer roller 102 are inrolling contact under pressure with media roller 104, the interactionzone 127 further defines a pressure nip 128. On the other hand, whenseam 116 of transfer roller 102 engages media roller 104, theinteraction zone 127 no longer defines a pressure nip 128 and theninteraction zone 127 generally refers to the overlapping position and/orengagement between transfer roller 102 and media roller 104.

In one embodiment, axis 124 allows rotation of cylinder 120 and is alsomovable via translation of axis 124 (as represented by arrow T) towardsand away from the rotatable (but otherwise fixed) axis 110 of transferroller 102. However, in another embodiment, rotatable axis 124 of mediaroller 104 is generally fixed to prevent its translation while rotatableaxis 110 of transfer roller 102 is also movable via translation towardand away from axis 124 of media roller 104. Accordingly, by moving axis124 of media roller 104 toward and away from axis 110 of transfer roller102 or by alternatively moving axis 110 of transfer roller 102 towardand away from axis 124 of media roller 104, one can vary the distancebetween media roller 104 and transfer roller 102.

With this in mind, media roller 104 is maintained in rolling contactunder pressure against transfer roller 102 such that media roller 104partially deforms blanket 114 of transfer roller 102 at pressure nip128, as later described in more detail in association with FIGS. 3-4. Inaddition, the pressure of media roller 104 against transfer roller 102is also indirectly measured by a gap (G) between cylinder 112 oftransfer roller 102 and media roller 104 (with media 122 or M carriedthereon), as also described in more detail in association with FIGS.3-4.

In addition to rollers 102 and 104, roller control system 100 includes acontrol manager 140 configured to control operation of transfer roller102 and media roller 104 as well as other rollers and functions ofprinter 12. As illustrated in FIG. 2, control manager 140 comprises acontroller 50 configured to generate control signals to operate rotationmotor 150 (to control rotation of both transfer roller 102 and mediaroller 104) and configured to generate control signals to operatetranslation motor 154 of media roller 104. In one aspect, the rotationmotor 150 also comprises one or more associated drives, gears, ortransmission mechanisms to enable control of the rotation of transferroller 102 and of media roller 104, respectively.

In one aspect, the translation motor 154 controls translation of mediaroller 104 relative to transfer roller 102 (as represented bydirectional arrow T) to move media roller 104 towards and away fromtransfer roller 102. In one aspect, translation motor 154 may alsocomprise one or more associated gears, drives or transmission mechanismsto cause translation of media roller 104.

As further shown in FIG. 2, an encoder 153 is associated with andcoupled to translation motor 154 and an encoder 152 is associated withrotation motor 150. In one aspect, encoder 152 indicates an angularposition of seam 116 of rotatable transfer roller 102 while encoder 153indicates a translational position of media roller 104 relative totransfer roller 102. With this arrangement, among other functions,control manager 140 is configured to generate control signals toimplement a gap setpoint based on the angular position of the seam 116of transfer roller 102 (as provided via encoder 152), as furtherdescribed below. Referring again to FIG. 2, it is understood that thesize of gap G (between the cylinder 112 of transfer roller 102 and mediaroller 104) is inferred via operation of encoder 153 associated withtranslation motor 154 of media roller 104. In addition, gap G remainsgenerally constant through non-seams areas 117 of the transfer roller102 that comprise a substantial majority of the circumference of thetransfer roller 102. In these non-seam areas 117, controller 50 acts tomaintain a generally constant gap G according to a generally constantgap setpoint based on feedback provided via encoder 153.

Nevertheless, it is further understood that in non-seam areas 117 agenerally constant difference remains between the gap setpoint and theactual gap G, even when the encoder based-adjustments perform optimally.In particular, the gap differential exists because of the previouslydescribed elastic properties of the coupling mechanism between thecylinder of the media roller and an axle of the translation motor 154 ofthe media roller. Accordingly the gap setpoint is generally equal to asum of the actual gap G and a previously described deformation of thecoupling mechanism 125 of media roller 104. In other words, the actualgap G is generally equal to the gap setpoint minus the previouslydescribed deformation.

In the conventional systems, the limited range of adjustments (asenabled by the encoder 153) and the relatively slow speed of makingthese adjustments is not adequate to compensate for the large force andposition disturbances caused by the seam 116 of transfer roller. Thisinadequacy is at least in part due to the very high speed of rotation ofthe transfer roller 102 and media roller 104 and also due to thedeformation of the coupling mechanism 125 of the media roller 104, whichintroduces a large imperfection in the position reading (inferred fromthe encoder 153) of the media roller 104.

With this relationship in mind, the difference between the actual gap Gand the gap setpoint can vary dramatically when seam 116 of transferroller 102 passes through interaction zone 127 with media roller 104(FIGS. 2-4), unless proper compensation is made to account for theelasticity of the coupling mechanism 125. In particular, in aconventional system, in the vicinity of seam 116 of transfer roller 104the effect of the force disturbance on the coupling mechanismsubstantially alters the actual gap G, thereby corresponding to asubstantial unwanted discrepancy between the actual gap G and the gapsetpoint (e.g., requested gap). In a conventional system, the unwantedpart of the substantial discrepancy (i.e. the part of the gapdiscrepancy that is in addition to the gap discrepancy already occurringin the non-seam areas 117) is left uncorrected, thereby resulting inlong-term damage to the blanket 114 and poor printing quality, amongother problems.

Accordingly, as later described in more detail in association with FIGS.5-8, in one embodiment of the present disclosure, controller 50 employsa gap setpoint profile 146, which is configured to apply a generallyconstant gap setpoint in non-seam areas 117 of transfer roller 102 andto temporarily increase the gap setpoint in the vicinity of the seam 116to thereby maintain a substantially uniform gap G between the mediaroller 104 and the cylinder 112 of transfer roller 102 (with partiallycompressed blanket 114 interposed therebetween) in the vicinity of theseam 116. In one aspect, the temporary increase in the gap setpoint istriggered based upon the angular position of seam 116 of rotatingtransfer roller 102. In particular, when the information from encoder152 indicates that the angular position of seam 116 is approaching lossof contact with media roller 104 in the interaction zone 127 (FIG. 2),control manager 140 causes the temporary increase in the gap setpointvia the gap setpoint profile 146. This temporary increase in the gapsetpoint compensates for the effect of the force disturbance that wouldotherwise occur in the vicinity of the seam 116 if a nominal gapsetpoint (i.e., the setpoint applied in non-seam areas 117) weremaintained about the entire circumference of the transfer roller 102.

By applying gap setpoint profile 146 to anticipate the force disturbanceat the seam area 116 (and the associated elastic deformation of thecoupling mechanism 125 of media roller 104), a substantially uniform gapG is maintained between transfer roller 102 and media roller 104.Moreover, by acting to maintain a substantially uniform gap G despiteseam areas 116, gap setpoint profile 146 (as applied via control manager140) provides a dynamic gap control mechanism to maintain asubstantially uniform pressure about the entire rotation of the transferroller 102, as later described in more detail in association with FIGS.5-8.

Controller 50 comprises one or more processing units and associatedmemories configured to generate control signals directing the operationof printer 12, including roller control system 100. In particular, inresponse to or based upon commands received via input 52 (as well asinformation provided via encoders 152, 153) or instructions contained inthe memory of controller 50, controller 50 generates control signalsdirecting operation of rotation motor 150 and translation motor 154 toselectively control the gap G between the transfer roller 102 and mediaroller 104. In one aspect, controller 50 automatically adjusts the gapsetpoint to accommodate the thickness of the media M so that the properamount of pressure (and corresponding actual gap G) is applied for eachof the different thicknesses of different types of media.

For purposes of this application, the term “processing unit” shall meana presently developed or future developed processing unit that executessequences of instructions contained in a memory. Execution of thesequences of instructions causes the processing unit to perform stepssuch as generating control signals. The instructions may be loaded in arandom access memory (RAM) for execution by the processing unit from aread only memory (ROM), a mass storage device, or some other persistentstorage. In other embodiments, hard wired circuitry may be used in placeof or in combination with software instructions to implement thefunctions described. For example, controller 50 may be embodied as partof one or more application-specific integrated circuits (ASICs). Unlessotherwise specifically noted, the controller is not limited to anyspecific combination of hardware circuitry and software, nor limited toany particular source for the instructions executed by the processingunit.

In another embodiment, an image sensor 130 is temporarily employedduring an evaluation phase of the printer 12 as a measurement tool inassociation with control system 100, as schematically depicted in FIG.2. Accordingly, in one embodiment, the image sensor 130 does not form aportion of printer 12 and is not present during normal operation ofprinter 12 after completion of the evaluation phase of printer 12. Inone embodiment, the sensor comprises a CCD laser displacement sensor. Inone aspect, during the evaluation phase image sensor 130 is used tomeasure the displacement of media roller 104 that occurs when seam 116of transfer roller 102 interacts with media roller 104. This measureddisplacement information is used to identify a gap setpoint profile thatwill maintain a substantially uniform gap G in seam area 116, as will befurther described later in association with FIGS. 5-8.

However, it is further understood that in another embodiment imagesensor 130 can be incorporated into printer 12 and be present duringnormal operation of printer 12 even though the image sensor 130 may ormay not further contribute to controlling the gap via a gap setpointprofile.

To better appreciate the “gap” being controlled between the media roller104 and the transfer roller 102, FIGS. 3 and 4 provide enlargedsectional views of one non-seam area 117 of transfer roller 102 and themedia roller 104 in the vicinity of the pressure nip 128, according toone embodiment of the present disclosure. As shown in FIG. 3, blanket114 has thickness (T1) and media (M) has a thickness (T2) such that withmedia roller 104 (with media M carried thereon) pressing againsttransfer roller 102, blanket 114 is compressed or deformed within thepressure nip 128. As further shown in FIG. 3, the portions 164 ofblanket 114 located outside of pressure nip 128 return to theiruncompressed thickness T1. Although not depicted in FIGS. 3-4, it willbe understood by those skilled in the art that a transition between thecompressed region and un-compressed regions 164 of blanket 114 istypically smoother than the transition shown in FIGS. 3 and 4.

FIG. 4 is an enlarged partial sectional view of transfer roller 102 withmedia roller 104 removed for illustrative purposes to demonstrate theamount of compression of blanket 114 and how gap G is defined relativeto the transfer roller 102 and the media roller 104. FIGS. 3-4illustrate cylinder 112 of transfer roller 102 having an outer surface119 while blanket 114 has an outer surface 164 and an inner surface 162.

As best seen in FIG. 4, the amount of compression of blanket 114 bymedia roller 104 (and with media M carried thereon) is represented by H.This compression is also indirectly measurable by the gap G between themedia M and the outer surface 119 of cylinder 112 because a sum of thegap G and the amount of compression (as represented by H) is generallyequal to the uncompressed thickness T1 of blanket 114. As illustrated inFIG. 4, dashed line 170 represents the outer surface of the blanket 114in the area of pressure nip 128 (if it were in an uncompressed state)while portion 172 represents the outer surface of blanket 114 whencompressed under pressure from media roller 104.

As illustrated by FIGS. 3 and 4, as non-seam areas 117 of transferroller 102 pass through pressure nip 128 (of interaction zone 127), thegap G is a measure of the deformation of the elastic blanket 114 of thetransfer roller 102 as media roller 104 is forced against the transferroller 102.

As will be understood by those skilled in the art from viewing FIGS.2-4, in a conventional system as seam 116 of transfer roller 102 passesthrough interaction zone 127, the gap G would change abruptly due to thechanging distance between the center of the rotational axis 110 oftransfer roller 102 and the center of the rotational axis 124 of mediaroller 104 in view of the substantially different topography of seam 116(FIG. 2) as compared to the generally smooth contour of non-seam areas117.

In contrast, embodiments of the present disclosure provide a dynamic gapcontrol mechanism to compensate for the change in distance between thecenter of the rotational axes 110, 124 related to the differenttopography of seam 116 and related to the elasticity of couplingmechanism 125, as further described later in association with FIGS. 5-8.This arrangement, in turn, minimizes abrupt changes in gap G in thevicinity of seam 116.

To better appreciate the elasticity of the coupling mechanism 125, FIG.5 provides a diagram 160 schematically illustrating a linear spring thatrepresent the elasticity (i.e., the metal compliance) of couplingmechanism 125 of media roller 104 when media roller 104 and transferroller 102 are in rolling contact under pressure by a force F. Asrepresented by FIG. 5, the gap setpoint for a given force F is generallyequal to an actual gap for the given force F plus the force F whendivided by the spring constant k (i.e. F/k). In other words, the actualgap G for a given force F is generally equal to the gap setpoint for thegiven force F minus the force F when divided by the spring constant k(i.e. F/k). In one aspect, the spring constant k represents theelasticity of linear spring 170, which in turn provides a model of theelastic behavior of the coupling mechanism 125 of media roller 104.Accordingly, even when operating in non-seam areas 117, there is agenerally constant difference between the gap setpoint and the actualgap due to the configuration of the coupling mechanism 125, which storeselastic energy in a manner similar to a linear spring as a result of theforce or pressure exerted between media roller 104 and transfer roller102. Moreover, this generally constant difference would remain even inthe ideal case of a perfect encoder-based control system (in which thecontrolled quantity would always be equal to the setpoint).

With these configurations in mind, FIGS. 6-7 will highlight a gapdifferential profile achieved via a gap setpoint profile, according toembodiments of the present disclosure. In particular, FIG. 6 is a graphillustrating a comparison of a conventional gap setpoint profile and agap setpoint profile produced according to one embodiment of the presentdisclosure. Meanwhile, FIG. 7 is a graph illustrating a comparison of aconventional gap differential profile and a gap differential profileachieved according to one embodiment of the present disclosure. In oneaspect, the gap differential represents the difference between the gapsetpoint and the actual gap G while accounting for the amount ofdeformation due to the elasticity of coupling mechanism 125 of mediaroller 104 (when under a constant force F between rollers 102 and 104).

As illustrated in FIG. 6, graph 250 comprises a pair of gap setpointprofiles 260, 270 plotted on a horizontal axis 252 representing time (inseconds) and a vertical axis 254 representing a gap setpoint (inmicrometers). This gap setpoint represents an input to achieve a desireddistance of separation (i.e., an actual gap G) between the cylinder 112of transfer roller 102 and media roller 104 (FIGS. 2-4). As illustratedin FIG. 6, certain landmarks of transfer roller 102 are identified inassociation with the gap setpoint profiles 260, 270. In particular,non-seam areas of the transfer roller 102 are represented by referencenumeral 117 (also seen in FIG. 2) while line 118 on graph 250 representsthe first edge of seam 116 (corresponding to a trailing edge of a mediaM), line 122 on graph 250 represents the intermediate portion of seam116, and line 120 on graph 250 represents the second edge of seam 116(generally corresponding to a leading edge of a media M).

As illustrated in FIG. 6, line 260 represents a conventional gapsetpoint profile which remains generally constant (e.g. 880 μm in oneexample) through non-seam areas 117 and as seam 116 passes through theinteraction zone 127 with media roller 104. Accordingly, in thisconventional profile no modification in the gap setpoint is made tocompensate for the force disturbance and position disturbance caused byseam 116 of transfer roller 102. The effect of maintaining thisgenerally constant gap setpoint as seam 116 passes through theinteraction zone 127 is illustrated in FIG. 7 by gap differentialprofile 322.

In particular, FIG. 7 comprises a graph 300 depicting a pair of gapdifferential profiles 320, 322 plotted on a horizontal axis 304(representing time in seconds) and a vertical axis 302 representing agap differential. In general terms, the gap differential is defined bythe actual gap G minus both a gap setpoint and the deformation ofcoupling mechanism 125 of media roller 104, as previously described.Conventional gap differential profile 322 reflects the response of theroller system to the conventional gap setpoint profile 260 of FIG. 6,which maintains a generally constant gap setpoint through the seam 116and which does not compensate for the mechanical deformation of couplingmechanism 125 of media roller 104 around the seam area 116. However, gapdifferential profile 320 in FIG. 7 corresponds to a gap setpoint profile270, in accordance with embodiments of the present disclosure, whichtemporarily alters a gap setpoint at seam 116 and which compensates forthe mechanical deformation of the coupling mechanism 125 of media roller104 around the seam area 116.

As shown in FIG. 7, conventional gap differential profile 322 comprisesa base value portion 350 representing the gap differential in non-seamareas 117 of transfer roller 102 which comprises a substantial majorityof the rolling contact between transfer roller 102 and media roller 104.

However, as media roller 104 passes by the first edge 118 of seam 116,both the position of the media roller 104 and the pressure between themedia roller 104 and transfer roller 102 will abruptly change as themedia roller 104 drops into the intermediate portion 122 of seam 116. Asthe pressure between the transfer roller 102 and media roller 104 isabruptly relieved, elastic energy stored in the coupling mechanism 125is abruptly released. These dramatic changes are reflected in FIG. 7 asthe gap differential of the conventional roller system abruptly plummetsfrom zero to about negative 160 micrometers (represented by portion352). This abrupt drop defines a maximum displacement of the rotationalaxis 124 of media roller 104 relative to the fixed rotational axis 110of transfer roller 102 when seam 116 passes through interaction zone 127(FIG. 2).

As further illustrated in FIG. 7, as intermediate portion 122 of seam116 passes through interaction zone 127 with media roller 104, thecoupling mechanism 125 initially experiences a generally dynamic stateof recovery with the gap differential eventually leveling off at nearnegative 120 micrometers (represented by portion 354) throughout amajority of the intermediate portion 122 of seam 116. However, with nopressure nip 128 functioning at this time within interaction zone 127,this relatively large gap differential does not directly affectprinting. However, FIG. 7 further illustrates that in this conventionalsystem the gap differential again changes abruptly as media roller 104bumps into the second edge 120 of seam 116, with the gap differentialquickly changing from near negative 120 micrometers to near zeromicrometers (represented by portion 356). In one aspect, this bumpingaction causes a large force disturbance between the transfer roller 102and the media roller 104 (FIG. 2-4). This results both in a rapiddeformation of the elastic blanket 114 (as blanket 114 becomes pinchedat the second edge 120 of seam 116) and in a rapid deformation of thecoupling mechanism 125 (via the compliance or elasticity of its metalcomponents) leading to an immediate displacement of media roller 104relative to the fixed transfer roller 102 and an abrupt change in theactual gap G.

This latter deformation of the coupling mechanism 125 is not sensed bythe encoder 153 and is the main contributor to the unwanted discrepancybetween actual gap and the gap setpoint. This elastic deformationprolongs the duration taken for the blanket 114 and for the couplingmechanism 125 to reach a steady-state equilibrium. Again, because theconventional encoder-based positioning mechanisms do not account for thevarying deformation of the coupling mechanism 125 when media roller 104engages seam areas 117 of transfer roller 102, significant unwanteddiscrepancies persist between the actual gap and the gap setpoint.

As further illustrated in FIG. 7, after the bumping action at the secondedge 120 of seam 116, several more hundredths of a second pass while thegap differential stabilizes (represented by portion 358) beforeeventually leveling off to a generally stable zero reading (representedby 360) as media roller 104 engages non-seam areas 117 of transferroller 102.

Accordingly, in a conventional system, the gap setpoint profile 260 inFIG. 7 remains generally constant (e.g., at 880 micrometers) while theactual gap G as measured by image sensor 130 (shown in FIG. 2)experiences large swings in value when the seam 116 of the transferroller 102 passes through interaction zone 127 with media roller 104, asdepicted by differential profile 322 illustrated in FIG. 7.

In stark contrast to a conventional system, FIG. 6 also illustrates agap setpoint profile 270, according to one embodiment of the presentdisclosure. In particular, gap setpoint profile 270 includes a basevalue 272 (e.g. 880 μm) for non-seam areas 117 of transfer roller 102, arising value segment 276 beginning near first edge 118 of seam 116 andcontinuing into intermediate portion 122, a peak value region 278 atintermediate portion 122 of seam 116, a falling value segment 280 nearsecond edge 120 of seam 116, and a base value 272 for non-seam areas 117after second edge 120.

This profile 270 depicts increasing the gap setpoint at seam 116 tocounteract or compensate for abrupt changes in the gap differential thatwould otherwise occur because of the elasticity of the couplingmechanism 125 of media roller 104, thereby maintaining a substantiallyuniform gap even in non-seam areas 117 immediately adjacent seam 116.Accordingly, as illustrated in FIG. 6, the increase in the gap setpointbegins near the first edge 118 of seam 116 and rises (as represented byrising segment 276) until reaching a peak in the intermediate portion122 (as represented by segment 278), and is decreased steadily as thesecond edge 120 of seam 116 passes through the interaction zone 127between media roller 104 and transfer roller 102 (as represented bysegment 280) but does not return to the base value 272 until sometimeafter the second edge 120 of seam 116 has passed beyond the interactionzone 127 with media roller 104.

Accordingly, in contrast to the constant gap setpoint in a conventionalgap setpoint profile 260, embodiments of the present disclosure employ agap setpoint profile 270 that maintains a substantially uniform firstgap setpoint (e.g., segments 272) in non-seam areas 117 but temporarilyincreases the gap setpoint (as represented by segments 276, 278, 280) toproduce a second gap setpoint in the vicinity of the seam 116.

FIG. 7 illustrates a gap differential profile 320 that represents theeffect of the gap setpoint profile 270 (FIG. 7), according to oneembodiment of the present disclosure. In general terms, the gapdifferential profile 320 reveals that the gap setpoint profile 270, inone embodiment of the present disclosure, produces a dramaticallydifferent gap differential profile than a conventional gap differentialprofile 322 corresponding to the conventional generally constant gapsetpoint profile 260.

As illustrated in FIG. 7, the gap setpoint profile 270 (shown in FIG. 6)produces a dramatically different response in the interaction betweenthe transfer roller 102 and the media roller 14 in the vicinity of seam116. In particular, a gap differential profile 320 (in embodiments ofthe present disclosure) reveals that the effect of the force disturbanceand position disturbance previously seen in the gap differential profile322 of the conventional system is circumvented in gap differentialprofile 320 by temporarily increasing the gap setpoint in the vicinityof seam 116. This increase in the gap setpoint directly compensates forthe change in deformation of the coupling mechanism of the media rollerthat would otherwise be caused by the force disturbance associated withthe seam(s) of the transfer roller.

As shown in FIG. 7, a gap differential profile 320 includes a basesegment 330 representing the gap differential in non-seam areas 117which extend throughout a substantial majority of the circumference ofthe transfer roller 102 that is in rolling contact with media roller 104and form pressure nip 128. However, as media roller 104 passes by thefirst edge 118 of seam 116, the gap differential of the roller systemdrops slightly from zero to about negative 40 micrometers (marked viaidentifier 332) before quickly rising (marked via identifier 334) to apositive value of near 40 micrometers (marked via identifier 336) asmedia roller 104 passes through the intermediate portion 122 of seam116.

The gap differential again decreases toward zero (marked via identifier337) as media roller 104 meets the second edge 120 of seam 116, with thegap differential rising briefly (marked via identifier 338) beforefalling back towards the base value (marked via identifier 340) asnon-seam areas 117 of the transfer roller 102 pass through the pressurenip 128. In particular, the gap differential eventually stabilizes at agenerally constant value again as both the coupling mechanism 125 anddeformation of the blanket 114 stabilizes, which in turn produces asubstantially uniform actual gap G (and substantially uniform pressure)about the circumference of the transfer roller 102 in the non-seam areas117 of the transfer roller 102. As illustrated in FIG. 7, dashed box 310identifies a seam-response zone in which there is a substantialreduction in the magnitude of the gap differential in the area of seam116 and in non-seam areas 117 immediately adjacent seam 116 as a resultof temporarily increasing the gap setpoint in seam 116, which in turnleads to a more uniform pressure profile in the vicinity of seam 116.

As illustrated in FIGS. 6-7, temporarily increasing the gap setpoint inseam area 116 minimizes the gap differential between the gap setpointand the actual gap by compensating for the deformation of the couplingmechanism 125 of media roller 104. This arrangement, in turn, enablesmaintaining a substantially uniform gap about the entire circumferenceof the transfer roller 102 and therefore enables maintaining asubstantially uniform pressure profile throughout the rotation of theentire circumference of the respective media and transfer rollers 104,102.

FIG. 8 illustrates a method 400 of determining a gap setpoint profile,according to one embodiment of the present disclosure. In oneembodiment, method 400 employs a system comprising substantially thesame features and attributes as the printer, components, and systems aspreviously described in association with the embodiments of the presentdisclosure illustrated in FIGS. 1-7. It is understood that thedetermining the gap setpoint profile is performed for a printer by firstapplying a substantially uniform gap setpoint (between the media rollerand the cylinder of the transfer roller) throughout a completerevolution of the transfer roller, even in the presence of seams such asseam 116 shown in FIG. 2. This determination is made in order toquantify the magnitude and the duration of disruption (from both forceand position disturbances) in the pressure and gap between the mediaroller and the transfer roller that is caused by the seam or recess ofthe transfer roller as the seam passes through the interaction zonebetween the transfer roller in the media roller. Based on the measuredmagnitude and duration of disruption, a gap setpoint profile isidentified that temporarily increases the gap setpoint in the vicinityof the seam of the transfer roller to avoid these disruptions. Aspreviously described in association with FIG. 2, the magnitude andduration of disruption is typically measured via an image sensor that istemporarily employed during this evaluation phase of the roller systemof the printer (and not present during normal operation of the printer).

Accordingly, in one embodiment, as shown at block 402, image sensing isused to determine the displacement of the media roller relative totransfer roller as the transfer roller rotates through severalrevolutions. The image sensing identifies patterns as to when, and byhow much, the media roller becomes displaced relative to the transferroller in the area of the seam. As illustrated in FIG. 7, in non-seamareas of the transfer roller, displacement of roller system has agenerally constant base value (as represented by segment 330) resultingin a substantially uniform gap G.

On the other hand, when the seam of the transfer roller passes throughthe interaction zone 127, a significant change of the gap differentialprofile 322 occurs, as illustrated in the seam-response region 310 ofFIG. 7. In one example, segments 352 and 356 of gap differential profile322 exhibit a large gap differential of a conventional system for thereasons previously explained in association with FIGS. 6-7.

As shown at block 404 in FIG. 8, method 400 includes identifying a timeinterval and/or angular position corresponding to the seam of thetransfer roller passing through the interaction zone between the mediaroller and the transfer roller. Accordingly, in one aspect, thedisplacement measurement information (obtained in block 402) is used toidentify an angular position of the media roller corresponding to whenthe seam of the transfer roller passes through the interaction zone. Inparticular, an angular position of the media roller is identifiedseparately for each of the landmarks associated with seam includingfirst edge, the intermediate portion, and the second edge. Bycorrelating the value of the gap differential with each of theselandmarks and the associated angular position of the media roller, onecan determine at which angular position the gap setpoint profile is tobe modified. Moreover, by viewing the gap differential for theconventional roller system, one can identify the maximum gapdifferential that occurs in the intermediate portion of seam. In oneembodiment, the timing and the magnitude of the temporary increase inthe gap setpoint should be set to generally correspond to the timing andthe magnitude of the undesired gap differential, except that the gapdifferential represents a negative value while the increase in the gapsetpoint is a positive value, as illustrated in FIGS. 6-7.

In other words, a maximum absolute value of the gap differential issubstantially equal to, and generally determines, the magnitude by whichthe gap setpoint is temporarily increased in the gap setpoint profile270 of FIG. 6. Accordingly, in one aspect, the increase of the gapsetpoint (e.g., gap setpoint profile 270 in FIG. 6) directly offsets thenegative value of the gap differential caused by not adjusting the gapsetpoint in the vicinity of seam 116 as illustrated by portion 352 ofprofile 322 in FIG. 8. In another aspect, the duration of the increasein the gap setpoint (e.g., gap setpoint profile 270 in FIG. 6) issubstantially equal to the duration of the negative value of the gapdifferential caused by not adjusting the gap setpoint in the vicinity ofseam 116 as illustrated by portion 352 of profile 322 in FIG. 7. Inanother embodiment, the maximum increase, and the duration of theincrease, in the gap setpoint profile 270 (FIG. 7) are selected to varyfrom the duration and the maximum absolute value of the gap differentialcaused by not adjusting the gap setpoint in the vicinity of seam 116 asillustrated by portion 352 of profile 322 in FIG. 7.

As illustrated in FIG. 6, by using this measurement information, theincrease in the gap setpoint (represented by portion 276) is set tobegin just prior to the first edge 118 of seam 116 and remainssubstantially greater than the base value 272 (at peak 278 anddecreasing portion 280) until the second edge 120 of the seam 116 passescompletely through interaction zone 127 when the gap setpoint returnsthe base value 272.

In another aspect, the displacement measurement information also revealsthe time interval or angular interval at which the large absolute valueof gap differential (i.e., maximum displacement) occurs. This timeinterval is also used to determine when to temporarily increase the gapsetpoint to counteract the force disturbances and position disturbancesthat would otherwise occur if a constant gap setpoint was maintainedwhen the seam 116 passes through the interaction zone 127.

Accordingly, as shown in FIG. 8, method 400 includes producing a gapsetpoint profile that maintains a substantially uniform gap in non-seamareas and temporarily increases the gap setpoint in seam areas based onthe time interval and angular position determined from the displacementmeasurement information, as shown at block 406.

As previously mentioned, embodiments of the present disclosure are notlimited solely to a media roller and a transfer roller in a printer butextend to the interaction of other combinations of rollers in rollingcontact with each other (in a printer) and in which a gap is to becontrolled between the two respective rollers with one or both of therespective rollers having one or more seams on their outer surface.

Embodiments of the present disclosure insure application of asubstantially uniform pressure at a pressure nip between a transferroller and a media roller despite large discontinuities, such as a seam,in a surface of the transfer roller or the media roller. Theseembodiments preserve the life and maintain the effectiveness of theblanket while increasing the quality of printing. These embodiments donot employ searching for obstacles or reacting to obstacles after theyare encountered. Instead, a gap setpoint profile is established for aroller system that automatically causes a temporary change in a gapsetpoint in anticipation of a seam of a transfer roller passing throughan interaction zone to enable the roller control system to successfullyoperate within its capacity limit (given the imperfection of theposition reading inferred from a conventional encoder coupled to theaxis of the translation motor).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A method of printing: providing a first roller that includes acylinder, an elastic outer portion at least partially covering thecylinder, and at least one seam; providing a gap in an interaction zone,between a second roller and the cylinder of the first roller, in whichthe respective rollers are in rolling contact under pressure; andcontrolling the gap, via selectively varying a position of one of thefirst roller and the second roller relative to the other respective oneof the first roller and the second roller, by temporarily increasing agap setpoint each time that the at least one seam passes through theinteraction zone, wherein at least one of the first roller or the mediaroller define a translatable roller.
 2. The method of claim 1 whereincontrolling the gap by temporarily increasing the gap setpointcomprises: defining a gap setpoint profile that includes: asubstantially uniform first gap setpoint when non-seam portions of thefirst roller pass through the interaction zone; and a second gapsetpoint, greater than the first gap setpoint, when the at least oneseam of the first roller passes through the interaction zone.
 3. Themethod of claim 2 wherein the at least one seam comprises at least onerecess and wherein providing the first roller comprises: arranging theat least one recess to include a first edge, a second edge, and anintermediate portion between the first edge and the second edge; andwherein defining the gap setpoint profile comprises arranging the secondgap setpoint to include: an increasing portion corresponding to passageof the first edge and of the intermediate portion of the at least onerecess through the interaction zone; a peak portion corresponding topassage of the intermediate portion of the at least one recess throughthe interaction zone; and a decreasing portion, after the peak portion,corresponding to passage of the intermediate portion and of the secondedge of the at least one recess through the interaction zone.
 4. Themethod of claim 2, comprising: determining the second gap setpoint byoperating the printer in a measurement mode including limiting theprinter to operation using the first gap setpoint about an entirecircumference of the first roller, including: identifying an angularposition of at least one of the second roller and the first roller thatcorresponds to passage of the at least one recess of the first rollerthrough the interaction zone; and identifying at least one of a timeinterval or an angular interval, based on the identified angularposition, at which the position of the rotational axis of thetranslatable roller is to be varied to implement the second gapsetpoint.
 5. The method of claim 4 wherein determining the second gapsetpoint includes: sensing a displacement of the movable rotational axisof the second roller relative to the fixed rotational axis of the firstroller to identify a displacement profile of the second roller;associating a maximum displacement on the displacement profile with theidentified time interval; and setting a peak value of the second gapsetpoint to be substantially equal to the maximum displacement of thesecond roller.
 6. The method of claim 4 wherein determining the secondgap setpoint includes: producing a gap differential profile for at leastone complete revolution of the first roller through the interactionzone, wherein a gap differential is generally equal to the first gapsetpoint minus a sum of an actual gap and a mechanical deformation of acoupling mechanism of the translatable roller; identifying a maximumabsolute value of the gap differential within the gap differentialprofile; and setting a peak value of the second gap setpoint to besubstantially equal to the maximum absolute value of the gapdifferential.
 7. The method of claim 1, wherein the at least one seamextends generally parallel to the rotational axis of the first rollerand comprises at least one of: at least one recess which extends throughthe outer portion; or at least one raised protrusion on the outerportion of the first roller.
 8. A printer comprising: a transfer rollerincluding a blanket and defining at least one seam extending generallyparallel to a longitudinal axis of the transfer roller; a media rollerpositioned for rolling contact against the blanket of the transferroller under pressure as a media passes through a nip between therespective rollers, wherein the blanket is under compression at the nip;and means for maintaining a substantially uniform pressure on theblanket as an entire circumference of the transfer roller passes througha location of the nip.
 9. The printer of claim 8 wherein the transferroller includes a cylinder with the blanket secured about the cylinder,and wherein the means for maintaining a substantially uniform pressurecomprises: a positioning mechanism configured to maintain asubstantially uniform gap between the media roller and the cylinder ofthe transfer roller via application of a first gap setpoint whennon-seam areas of the transfer roller pass through the nip and viaapplication of a second gap setpoint, greater than the first gapsetpoint, when the at least one seam of the transfer roller passesthrough a location of the nip at which no printing occurs.
 10. Theprinter of claim 9 wherein the positioning mechanism comprises at leastone of the transfer roller or the media roller including a rotationalaxis having a fixed position and the other one of the respective mediaroller and transfer roller including a rotational axis having atranslatable position.
 11. The printer of claim 10 wherein thepositioning mechanism comprises: a translation motor configured to causetranslation of the translatable rotational axis to vary the position ofthe media roller and the transfer roller relative to each other; anencoder associated with, and configured to measure translation of, thetranslatable rotational axis; and a controller configured to operate thetranslation motor according to a gap setpoint profile to achieve thesubstantially uniform gap, wherein the gap setpoint profile includes:applying the first gap setpoint in the non-seam areas, via feedback fromthe encoder, to achieve the substantially uniform gap in the non-seamareas; and applying the second gap setpoint at the at least one seam,via predefined image-based displacement information regarding thetranslatable rotational axis and via feedback from the encoder, tosubstantially achieve the substantially uniform gap at the at least oneseam.
 12. The printer of claim 11 wherein the predefined image-baseddisplacement information is determined during an evaluation phase of theprinter and then is subsequently employed as a fixed operating parameterof the printer and of other substantially similar printers, wherein thepredefined image-based displacement information is determined viaoperating the printer in the evaluation phase exclusively with the firstgap setpoint and without the second gap setpoint, and wherein thepredefined, image-based displacement information is associated with theat least one seam passing through the location of the nip and includes amagnitude of, and a duration of, the displacement of the translatablerotational axis of one of the media and transfer rollers relative to therotational axis of the other respective one of the media and transferrollers.
 13. The printer of claim 8 wherein the printer comprises: animaging roller in rolling contact under pressure against the transferroller; a charging station configured to cause a substantially uniformlycharged surface on the imaging roller; an imager configured to dischargethe surface of the imaging roller in a pattern corresponding to animage; and a developing station configured to apply ink to thedischarged portion of the surface of the imaging roller to form an inkedimage, wherein the inked image carried on the surface of the imagingroller is transferred onto the blanket of the transfer roller via therolling contact between the image roller and the transfer roller andalso transferred onto the media via the rolling contact between thetransfer roller and the media roller.
 14. A printer comprising: atransfer roller including a blanket surrounding a cylinder and definingat least one seam extending generally parallel to a longitudinal axis ofthe transfer roller; a media roller positioned for rolling contact underpressure against the blanket of the transfer roller as a media passesthrough an interaction zone between the respective rollers with themedia roller causing at least partial deformation of the blanket of thetransfer roller; and a controller configured to apply a gap setpoint toproduce a substantially uniform gap between the cylinder of the transferroller and the media roller throughout a rotation of an entirecircumference of the transfer roller, wherein the controller isconfigured to set a base value of the gap setpoint that is applied to asubstantial majority of the circumference of the transfer roller and toset a second value of the gap setpoint that is applied at the at leastone seam of the transfer roller, wherein the second value issubstantially greater than the base value.
 15. The printer of claim 14wherein the media roller includes a rotational axis and an encoderassociated with, and configured to measure translation of, therotational axis, wherein the substantially uniform gap is maintainedusing feedback from the encoder to the controller, and wherein thesecond value of the gap setpoint is determined during an evaluationphase prior to operation of the printer and is obtained via use of animage sensor to measure a displacement of the media roller relative tothe transfer roller when the at least one seam passes through theinteraction zone with the base value of the gap setpoint being appliedthroughout the rotation of the entire circumference of the transferroller during the evaluation phase.